In an air separation plant comprising one or more series of air compressors and one or more cold boxes, the air compressors have fixed functions which do not vary in accordance with the operating modes of the plant. In particular, an air compressor compresses the air from atmospheric pressure up to a delivery pressure substantially the same as that of the distillation column having the highest pressure. A booster compressor compresses air from this delivery pressure of the air compressor to a delivery pressure defined by a combination of the pressure for vaporization of the oxygen and/or the liquid nitrogen and the quantity of liquid products to be produced.
FR-A-2895068 describes an air separation plant comprising two air compressors receiving air at a pressure substantially equal to atmospheric pressure, two air purification units and two cold boxes. Each compressor is connected to each of the purification units so as to send compressed air thereto, the purification units being each connected to two cold boxes. A first of the compressors is designed to produce air at a first pressure and send the air at the first pressure to a first purification unit and the first purification unit is connected to high-pressure air lines of a first cold box. A second compressor is designed to produce air at a second pressure, lower than the first pressure, and send the air at the second pressure to a second purification unit and the second purification unit is connected to medium-pressure air lines of the second cold box.
With this process it is not possible to continue operation of an air separation apparatus supplied with the purified high-pressure air when the only compressor supplying high-pressure air during normal operation and/or the only purification unit supplying purified high-pressure air during normal operation produces less air than expected or is not in working order.